Dennis R. Kerr

Sequence Stratigraphy of the Middle Pennsylvanian Bartlesville Sandstone, Northeastern Oklahoma: A Case of an Underfilled Incised Valley

The Middle Pennsylvanian Bartlesville sandstone, a prominent oil producer in Oklahoma over the past 90 yr, is evaluated in terms of its sequence stratigraphic architecture over its occurrence in northeastern Oklahoma. The Bartlesville sandstone is interpreted to be a fluvial-dominated incised-valley fill deposited mainly during rising stages of relative sea level.

Recognition and Implications of Volcanic Glass Detritus in the Fluvial Deposits of the Middle Frio Formation, South Texas

ABSTRACT Detrital volcanic glass has been identified in fluvial deposits of the middle Frio Formation of South Texas. Petrographic analysis of core samples from Seeligson and Stratton fields reveals abundant unabraded to slightly abraded, very fine sand- to silt-sized glass shards. Gamma-ray log response correlates with the presence of volcanic glass. Volcanic glass and API unit counts markedly increase through the medial third of the middle Frio and diminish toward the upper third of the middle Frio. The stratigraphic and aerial distribution of volcanic glass detritus in middle Frio sandstones and mudstones suggests that volcanic ash was deposited rapidly on the Oligocene coastal plain of South Texas. Ash was apparently also deposited in the catchment basin of fluvial systems delivering sand to the Stratton area. Given the regional biostratigraphic constraints of middle Frio fluvial deposits, the interval containing volcanic glass is regarded as representing the 30- to 34-mya eruptive event in the Trans-Pecos region.

Integrated Approach Towards the Application of Horizontal Wells to Improve Waterflooding Performance

This report is funded under the Department of Energys Class I program which is targeted towards improving the reservoir performance of mature oil fields located in fluvially dominated deltaic geological environments. The project involves using an integrated approach to characterize the reservoir followed by proposing an approach reservoir management strategy to improve the field performance. In the first stage of the project, the type of data integrated includes cross bore hole seismic surveys, geological interpretation based on the logs and the cores, and the engineering information. In contrast, during the second stage of the project, it was intended to use only conventional data to construct the reservoir description. This report covers the results of the implementation from the first state of the project. It also discusses the work accomplished so far to the second stage of the project . The production from the Shelf Unit (location of Stage I) has sustained a significant increase over more than three years.

Diagenetic Variability in Middle Frio Formation Gas Reservoirs (Oligocene), Seeligson and Stratton Fields, South Texas

ABSTRACT Two distinct reservoir types (type I and type II), differentiated on the basis of framework mineralogy, diagenetic history, and reservoir quality, are present in the Oligocene middle Frio Formation in Seeligson and Stratton fields, South Texas. Type I reservoir sandstones are feldspathic litharenites to litharenites having an average composition of Q30F25L45. Lithic fragments are predominantly volcanic and carbonate rock fragments. These sandstones underwent early calcite precipitation, after which secondary porosity developed (dissolution of feldspar, rock fragments, and calcite cement). Kaolinite or chlorite and pyrite postdate secondary porosity and locally influence porosity and permeability trends. Porosity averages 20% and ranges between 7% and 28%. Permeability averages 400 md and ranges between 0.007 md and 4,000 md. The large variation in porosity and permeability in these gas reservoirs is directly related to the irregular distribution of calcite cement and the development of secondary porosity. Type II reservoir sandstones, which occur in the medial third of the 2,000- to 2,500-ft thick (600- to 760-m) middle Frio Formation, are lithic arkoses to feldspathic litharenites having an average composition of Q28F31R41. Lithic fragments are predominantly volcanic rock fragments; carbonate rock fragments are rare. These sandstones contain abundant unabraded to slightly abraded glass shards and volcanic ash matrix. Devitrification of volcanic glass detritus has resulted in analcime precipitation, which precedes and overlaps in time with an early calcite cement phase similar to that found in type I reservoirs. Secondary porosity, which developed through the preferential dissolution of volcanic glass and feldspar, postdates these cementation events and has resulted in the development of moldic and intragranular porosity that can be as high as 18%. Mixed-layer illite-smectite lines much of the secondary pores. Porosimeter porosity averages 18% and ranges between 5% and 27%. Permeability averages 5.5 md and ranges between 0.005 md and 78 md. Although average porosity in type II reservoirs is similar to that in type I reservoirs, much of it is ineffective. The precipitation of calcite and analcime in intergranular pores and illite-smectite in secondary pores, combined with abundant volcanic ash matrix, results in poor communication between pores and a corresponding decrease in reservoir quality.